In the last two decades, there has been tremendous progress in combining micro-electronics with miniature mechanical devices to achieve various functionalities that could not be implemented on a regular scale. Leveraging the micro-fabrication techniques for Si-based integrated circuits, electronics and micrometer-sized mechanical elements, sensors, and actuators can be integrated on a common substrate to produce micro-electro-mechanical system (MEMS) devices. MEMS devices have found wide applications in aerospace, automotive, biotechnology, robotics, and consumer electronics. As an example, many display devices based on the DLP projection technology use a digital micro-mirror device (DMD) chip, which is a MEMS device that has on its surface several hundred thousand micro-mirrors corresponding to the pixels of the display. The orientation of each micro-mirror can be individually controlled to alter how the mirror reflects the light from a light source.
As the trend of miniaturization continues, the frontier of fabricating miniaturized devices has now moved to the nanometer scale, with the dimensions of the electronic and mechanical elements of a nano-electro-mechanical system (NEMS) device often measured in nanometers or tens of nanometers. Compared to MEMS devices, NEMS devices have the potential of offering new functionalities not only due to the orders-of-magnitude smaller device sizes but also for the reason that nano-scale devices can exhibit physical phenomena that are quite different from those at the micro-scale.
One major challenge in developing NEMS devices, however, is the difficulty in providing a suitable actuation mechanism for operating nano-scale mechanical devices. Actuation mechanisms used in MEMS devices typically cannot be readily scaled down to the nano-scale while maintaining their operability or individual addressability. It has been proposed to use piezoelectric materials to form nano-scale actuators, but such piezoelectric components are difficult and expensive to fabricate on the nano-scale.